The invention relates to a picture display cell comprising as a substrate two orthogonally relocated plates which are transparent to light and which on the facing sides comprise an electrode of a material which is transparent to light and having an orientation layer, a sealing ring positioned between the ends of the plates, a liquid crystalline material being provided in the space between the plates and the ring. The invention further relates to a method of forming an orientation layer on a substrate for the picture display cell comprising an electrode and to the materials from which the orientation layer is manufactured.
Such a picture display cell is known from U.S. Pat. No. 4,469,409 in which picture display cell an orientation layer is provided on a glass substrate, which orientation layer is formed from a film of a homogeneous mixture having a silanol oligomer modified with an aromatic ring which comprises a silane group and an organic polymer. The picture display cell of the twisted nematic type (TN-type) according to the said U.S. Patent comprises a substrate having an orientation layer which can withstand elevated temperatures better and bonds more satisfactorily to the substrate in the previously used organic polymers having an imide or quinazoline ring and bonds more satisfactorily in the substrate. A method of providing a polymeric layer on a substrate is described in example 1 of this U.S. Patent in which a solution of the polymer is prepared and this solution is provided on the substrate via a spinning technique.
German Auslegeschrift 2,315,541 discloses a picture display cell in which on the substrate an orientation layer is provided by vapour deposition at reduced pressure. According to this vapour deposition technique SiO.sub.x layers are provided. More information on such layers is shown in H. A. van Sprang and R. G. Aartsen in J. Appl. Phys. 56 (2), July 15, 1984, pp. 251-262, in which article the method of providing, the measurements and the apparatus used are described.
The use of such an SiO.sub.x orientation layer in a picture display cell, however, has for a disadvantage or in that with these cells only a restricted range of solid angles for the orientation of the nematic liquid crystal material is available.
German Offenlegungschrift 3,020,645 discloses a picture display cell in which a polymeric orientation layer is provided on the substrate, which polymeric orientation layer itself is liquid crystalline. When switching on or off the voltage the liquid crystalline material and the polymeric layer are both oriented at right angles to or parallel to the substrate. The orientation layer is also in the liquid crystalline phase under operating conditions.
Japanese Patent Application Kokai No. 52-146255 discloses a picture display cell having a liquid crystalline material in which the orientation of the liquid crystalline material takes place by incorporating herein magnetic particles, for example, --Fe.sub.2 O.sub.3 acicular particles which are oriented by means of a magnet, after which the temperature of the glass plates is raised so that the liquid binder at the raised temperature is made to solidify. In this manner the magnetic particles are fixed and hence also the liquid crystal material. The presence of the acicular --Fe.sub.2 O.sub.3 -particles in the picture display cell, however, has disadvantages because under the influence of said particles inteferences in the light permeability can easily occur.
Applicants have made further research into the orientation layer of the picture display cell and they have found that it is possible to provide a polymeric layer on the substrate, which polymeric layer can be oriented and fixed after the orientation. As specific examples of polymers that may be used are the specific materials described inter alia by R. Simon and H. J. Coles in Mol. Cryst. Liq. Cryst. Vol. 102 (Letters), pp. 43-48. This method yielded good results but had the disadvantage that it took some time, for example, 5 minutes to more than 1 hour, dependent on the polymer used, until the orientation layer had been oriented completely in an electric or magnetic field.